text:
Can the pilot stop airflow between cockpit and cabin?
During normal operation the entire fuselage is pressurized equally:

An aircraft fuselage does not contain separate compartments with different pressure values in each. The entire vessel is pressurized equally from the forward pressure bulkhead to the aft pressure bulkhead. This normally includes the cabin, cockpit, and lower-deck cargo holds. (source)

If my understanding of physics is correct, this means that there must be airflow between the cockpit and the cabin (otherwise a pressure difference would occur). The airflow equalizes the atmospheric pressure in the cockpit and cabin.
Question: Can the pilot completely stop the airflow between cockpit and cabin, i.e. hermetically sealing off the cockpit from the cabin ?
3 scenarios for which this question is interesting:

fire
If there is smoke in the cabin, the pilot would need to prevent the smoke from entering the cockpit.
hull breach
Does cabin depressurization (due to a hull breach for example) directly lead to cockpit depressurization? Or can the pilot prevent this by stopping the air outflow from the cockpit to the cabin?
MH370
One working hypothesis in the MH370 mystery is accidental or deliberate cabin depressurization. Assuming the latter, is there any way the perpetrator in the cockpit could prevent the cockpit depressurization ?

I would appreciate if your answers included these 3 scenarios. Since the third scenario deals with a B777, please use this type as an example. Technical airflow diagrams very welcome!

Concerning scenario 1 (fire), my research into this question seems to suggest, that the cockpit is indeed designed to be sealed off in case of fire. I could not find the relevant information for a Boeing-777, but here is a description of how smoke entered the MD-11 cockpit in the Swissair 111 crash and how it was supposed to be prevented (smoke barrier, etc):
SR 111 Investigation Report:

Airflow patterns in the MD-11 are affected by the aircraft configuration. In the forward portion of the aircraft, this configuration includes the valve position of individual air outlets in the cockpit and throughout the cabin, and the position of the louvres in the bottom part of the cockpit door. Also, all MD-11s are equipped with a smoke barrier installed laterally across the aircraft in the attic area above the cockpit aft wall (see figure 3). Inspection of Swissair MD-11s showed that the smoke barrier was sealed relatively tightly in some aircraft, while in others there were gaps in the barrier at the edges and at the seams where conditioned air ducts pass through the barrier. These gaps allowed air to flow past the smoke barrier. The holes in the barrier, designed to permit the engine fire shut-off cables to pass through the barrier, would also be a path for smoke to pass between the cabin and cockpit.

Possible duplicate of If the pilot cabin loses pressure, can the pressure difference lock the cockpit door?. Perhaps not an exact dupe but the answers will be the same.

This is a completely different question. And answers applicable over there would not in the slightest answer this question here.

Related

fire If there is smoke in the cabin, the pilot would need to prevent
  the smoke from entering the cockpit.

This is a bit more complex as the cockpit door by its own nature will slow the flow of smoke but will not stop it all together. Smoke flow is also dependent on the movement of air within the aircraft. In your example of SR-111 the smoke was not in the cabin but in the overhead section so closing the cabin door would not have accomplished much. While smoke barriers are installed ultimately in a fire situation its only a matter of time before another hole is burned through. This is why early identification and extinguishing is so key. By the nature of cockpits things like wire bundles, cable chases, and at one time in history control cables must come and go so you cant truly seal a cockpit anyway.

hull breach Does cabin depressurization (due to a hull breach for
  example) directly lead to cockpit depressurization? Or can the pilot
  prevent this by stopping the air outflow from the cockpit to the
  cabin?
MH370 One working hypothesis in the MH370 mystery is accidental or
  deliberate cabin depressurization. Assuming the latter, is there any
  way the perpetrator in the cockpit could prevent the cockpit
  depressurization ?

You can generally lump these into the more general question of "can the cockpit be pressurized separately from the rest of the aircraft" to which the broad answer is no. Simplly put the cockpit door is not capable of serving as a bulkhead and cant withstand the pressure differential, as far as I know they also lack any sort of sealing, bracketing or joints for such a task. The only aircraft I can really think of that ever had a feature like this was the B29 Super fortress which had independent fore and aft sections that were independently pressurized. This allowed an unpressurized bomb bay in the center. To make this possible both sections had small pressure doors to allow entry.

(source)
The only thing a flight crew could do, is potentially depressurize the whole aircraft and use the pilot and co-pilot 02 system to outlast the cabin 02 masks, then decent below FL100 and breathe normally.


text:
How to refute this geometrical method to find MH370?
A geometrical method to find MH370 has been published on the Net (see images below).
I am sure it is wrong (because if it were that easy, thousands of people would have had this idea back in 2014). However, it has attracted some attention.
My question is:
How can this method be proven wrong in a simple, straight-forward way ?

Here is the method:

source: This method was first presented here.
EDIT:
How is this question off-topic while How can a computer model yield two possible flight paths of MH370 in South Indian Ocean? is on-topic? Isn't this having it both ways?

The final ping is not at the crash site.  The Pings were done at an interval of once an hour.  So after the final ping, the plane may have crashed immediately, or may have flown for almost another hour before crashing.  That time-window alone creates huge uncertainty.

I don’t quite understand the step that creates the congruent rings around point B... anyone?

An 84km "margin of error" is more than 22,000 square kilometers, roughly the size of the country of Belize. Expand that based on up to an additional hour of travel (in any direction, planes can turn quickly) and you are looking at potential search areas in the millions of square kilometers.

"Once we have reliable takeoff and crash locations it is fairly easy to determine exactly where it crashed" ?? Looks like a truism.

@ron-beyer: your comment is true, but besides the point, because (1) it doesn't answer the question and (2) determining MH370's resting place with a margin of error of 84km would be a HUGE step forward compared to what we currently know. Calculate the margin of error of the entire 7th arc + add 1 hour of travel and please state what fraction of that 22k km² is. It doesn't matter anyway, since the method is wrong. The question was to demonstrate that it is wrong.

@abelenky: No, MH370 could NOT have "flown for almost another hour before crashing" after the 7th arc, because (1) the fuel wouldn't last for 1 hour after the time of the last Inmarsat ping, (2) the final BFO values indicate not only a steep dive, but a steep dive with increasing RoD, (3) the lack of IFE relogon is due to fuel exhaustion. You cannot fly for 1 hour without fuel.

@mins: yes the phrase is awkward. Seeing that "crash locations" is plural, I assume that "a set of possible crash locations" (i.e. a circle) is what was meant, but I'm not 100% sure.

@CptReynolds: To get B: draw a line from A (Inmarsat 3F1 subsatellite point) through KUL. B is twice as far away from the subsatellite point as KUL. // Then draw circles around B with the same radius as the circles around A. Was that your question?

@rainbowtableturner I got that, but what is the logic behind that geometric exercise? Why is point B relevant to the crash location? I may miss something very obvious, but I still don’t see the method behind it...

What sort of refutation are you looking for? If I said that I found MH370 and buried it in my back yard, what would you consider to be a refutation of that?

@TannerSwett: Is your backyard in Indian Ocean close to the 7th arc south of KUL and within fuel constraints? No. So based on that alone your claim can be refuted. But more to the point: The method above does not claim that it COULD be at the southern green dot (which might even be true by chance/accident although the method is wrong), but that it can ONLY be there. So from a scientific point of view, I think there are 2 possible ways to refute the method: (1) prove that MH370 can be elsewhere or (2) prove that the method itself is wrong.

@CptReynolds: I agree with you. I don't see any apparent mathematical concept (but just because I don't see it, doesn't mean there isn't any). It's just that geometrically it looks intriguing and I can see how it would have an appeal to people with low or below average mathematical/geometrical skills. It's not by accident, that the method was posted on the DailyStar of all places. I would just like to be able to explain in simple terms to exactly this kind of public with low maths skills attracted to the model, why it MUST be wrong.

<How is this question off-topic while How can a computer model yield two possible flight paths of MH370 in South Indian Ocean? is on-topic? You can't have it both ways.> Yes, we can. The question you link asks to explain the methods used by an official investigation. Official investigations are on topic here. You ask us to "(dis)prove" some sort of badly defined/justified method a random person on the internet came up with. We are not here for that.

@Federico: Thank you for explaining the rationale.

This question is also too unclear to answer, because you're asking us to disprove "this method", but you're not telling us what the method is.

@TannerSwett: I did tell you what the method is, i.e. how it works. I did not tell you the author's rationale, simply because I don't know it myself and it is not necessary to prove or disprove the method. Just to illustrate this point, think of a method to determine the speed of light. You may not understand why the method works/doesn't work, but you can still prove it right/wrong.

@rainbowtableturner The reason you don't understand the method is the same as the reason why we can't disprove it: because the post is simply rubbish. The diagrams are just made up and covered with impressive sounding words.

@DJClayworth: Your comment lacks scientific rigor. I have outlined above that a method can be proven wrong regardless of the level of understanding and I mentioned 2 ways to do that. There may be others. Saying "it is simply rubbish" is neither scientific nor proves/disproves anything.

If I say that MH370 can be found by "zoogblat infrkwt hrrtyyflppq" can you please disprove that theory? I don't understand it but I've told you the method. If you can disprove that, then I will work on disproving your theory.

The diagram is clear that the blue dot is the departure point, and A is the satellite.  But what the heck is B (congruent)?  It seems to be some random point with no basis for selecting it.

You could ask this question over at the mathematics stack exchange.

Maybe they are trying to say that those are the only two points which are a seven hour flight's distance away from the point of departure (assuming that they flew in a straight line) and are on the circle of the 7th ping?  If so, they are making the assumption that they didn't turn and also that there was no wind (which would cause the two points to not be the same distance from the departure point like in the diagram).  I'm sure there are other issues, but that immediately springs to mind.

The picture says that "If [the above facts are] true, the plane can only be at one of two green dot locations." However, it doesn't give any reasoning or evidence to support this claim. So, there's no reason to think that the claim is correct.
You asked if itʼs possible to prove that the method is wrong. Itʼs not possible to prove that the method is wrong, because there is no method here. The picture is merely a collection of facts and unsupported claims.
However, the picture does seem to rely on a particular premise. Specifically, the picture seems to be based on the premise that the departure airport, the Inmarsat satellite, and the crash site must form a right triangle. That premise is false; the locations of airplane crashes are actually not affected by the positions of overhead satellites (or vice versa).

No evidence is presented for items 1-3, but that doesn't by itself make item 4 wrong. Particularly as items 1-3 are generally accepted knowledge (and the consensus on wikipedia). Item 3 should probably be modified to say "on or close to the 7th arc"

Even if you assume that items 1 through 3 are correct, no evidence or reasoning is given for item 4.

I agree. But that doesn't necessarily make item 4 wrong. Therefore it can't be used as proof that item 4 is wrong.

@rainbowtableturner Yes it’s no proof 4 is wrong. But with equal confidence one could state „1-3 are true. Therefore it must be at Area 51.“ since no deduction is given that allows to get to 4 from 1-3, right?

No. Area51 is nowhere near the 7th arc.

@rainbowtableturner Yes, of course.

@CptReynolds: I agree though, that the deduction is left unexplained. My intention of posing the question, however, is – absent such explanation – to prove the method itself wrong or right.

"the locations of airplane crashes are actually not determined by the positions of overhead satellites" no, that statement is actually false. Crash sites can be and actually are determined by position of overhead satellites. It is called triangulation and you need at least 3 satellites. If you have less than 3 but other additional data, it might also be possible (by other methods than triangulation). In this case we have 1 satellite, which gives us an arc (which IS determined by the satellite position). The claim is that the additional data is enough to narrow down the location.

When I wrote "the locations of airplane crashes are actually not determined by the positions of overhead satellites", what I meant is that wherever a satellite is, the satellite does not cause planes to crash in a particular place. I've edited my answer to try to make that clearer.

"I meant is that wherever a satellite is, the satellite does not cause planes to crash in a particular place" uhm ... nobody ever said that

@summerrain You're making me feel very frustrated right now. You asked us to "refute this method", even though there's no method described here to refute. So I take my best guess at what the method is, and now you respond to my guess by saying "nobody ever said that". Multiple people have tried to help you multiple times in multiple ways, and you've done nothing but complain about our answers and say that we're wrong. If you want more help, then please show some gratitude and some effort.

@TannerSwett: please don't talk about me but about the issue/question at hand. You said that "the satellite does not cause planes to crash in a particular place". Satellites don't cause planes to crash, period. That's obvious and nobody made that claim. I don't understand what gratitude you want to receive for refuting claims nobody made? I'm honestly lost.

@summerrain What I said is that the picture seems to rely on the premise that satellites cause planes to crash in a particular place. Yet, as you know, satellites don't actually do that. So, the premise that the picture seems to rely on is false. Maybe the picture isn't relying on that premise at all, but in that case, the picture seems to be absolute nonsense. I have no way to refute absolute nonsense besides pointing out that it seems to be absolute nonsense.

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text:
How does maximum speed vary with altitude?
Question: How does a commercial jetliner's highest possible groundspeed vary with altitude (assuming wind=0) ?
My understanding is that drag decreases with altitude, therefore maxspeed increases with altitude.
This is also what Cpt. Simon Hardy, a B777 instructor, says:

« Aircraft [referring to airliners] go faster at altitude than at low
  level. At sea level the aircraft [referring to a B777] can only do 330
  kn. And at altitude, 30.000 ft, it can do Mach 0.86. So it's a sort of
  sliding scale – as you descend, you get slower. » (source)

But today I read exactly the opposite on an aviation blog, which I found curious:

« When a plane gets so high, you have to fly slower, since the speed of sound (and hence true airspeed for a given Mach number) decreases with altitude. » (paraphrasing, source)
« Real basic point: You’re flying higher, you’re flying slower. You want to go fast […] you just fly lower. » (source)

... so which is it ?
The perfect answer for me would ...
• include a graph (Y: altitude, X: maxspeed)
• include citable references

EDIT (in response to the comments below):
I specified maxspeed as the highest possible groundspeed (assuming wind=0), although I'd rather prefer not to make that distinction, because from my experience this complicates the issue more than necessary: Of course the altitude will affect the different types of speed more or less, but isn't it nonetheless possible to make an approximate statement like "higher=faster, lower=slower" and explain why that is?
EDIT2
For a concrete example, let's assume:

aircraft = B777
wind = 0 km/h (for argument's sake)
weight = typical weight of a B777 ~45min into a 9 hour long haul flight
aircraft has already reached cruising altitude

If at that point the pilot wanted to "get away" as fast as possible (let's say from waypoint IGARI), what altitude should be chosen?
Is the quoted blog post correct in saying that at an usually high altitude, the plane would fly slower, therefore it would have to go lower to fly faster?

This very much depends on what kind of speed you are referring to. IAS, TAS, Mach, etc. There are a number of questions on the site which explain the differences and their interaction.

Also, are you asking maximum possible speed (if yes, there will be a discussion on what that means and what side assumptions you wish to make) or maximum certified (i.e. permitted) speed?

@TomMcW and Cpt Reynolds: I edited my question in light of your comments. And I don't ask about their interaction.

BTW speed of sound TAS varies with temperature, NOT altitude (air density)

Your edited statement: it's certainly possible to make a vague/general statement like "higher/faster, lower/slower" and explain why that is. I would say that this is NOT possible without defining a specific speed type.  IAS = higher/slower, but TAS = higher/faster (everything else being equal).  So, which do you want? (each individual type of speed is discussed elsewhere on this site)

@CptReynolds: I am inquiring about the maximum possible speed, however I am not asking how fast that speed is, but if it increases or decreases with altitude.

@Jimmy: re: "IAS = higher/slower, but TAS = higher/faster" Are you saying that maximum TAS increases with altitude, but maximum IAS decreases with altitude?

@rainbowtableturner Ok, that works. Are parts of the aircraft allowed to break off in your scenario or not?

Yes, that’s what I’m saying. Which is why your request to provide a simple graph cannot be done without defining which type of speed is applied.

@CptReynolds: they shouldn't :-)

That's the rub.  TAS is the actual speed and relates to Mach.  Indicated airspeed is the   stress on the airframe from aerodynamic forces and is dependent on TAS and altitude.  The higher you go, the lower IAS is for a given TAS. Once IAS Mach limit is LESS than IAS to reach Vne, your "speed limit" is Mach.  At a lower altitude, your "speed limit" is IAS Vne, and you get there BEFORE you reach Mach limit.  See upper right hand corner of Boeing 777 graph below.

This question isn't clear because "speed" means different things to different people, and this is also engine specific.  Every aircraft will have a different speed vs altitude profile.  In general...
Mach will go up, as you increase in altitude.  This is because the lower density air lowers the speed of sound (in an absolute sense).
True airspeed will go up as you maintain a constant indicated airspeed.  Conversely, maintaining a constant true airspeed will increase your indicated airspeed as you descend.
Normally, a jetliner should not be seeing true air speed at sea level.  For jetliners, even if your engines are good enough to get you there, the aircraft has an indicated airspeed structural limit that keeps you from accelerating.  You can keep the same speed (at structural limit) through higher altitude, which increases your TAS.
There is a chart here which should help show the relationships between altitude and speed:
A simplified chart for determining Mach number and true airspeed from airspeed-indicator readings:

"Mach will go up, as you increase in altitude." TAS also? Your chart is helpful. But I don't know how to read the TAS vs altitude relationship. A simpler chart with only these two on X/Y would help me understand.

There is no TAS/altitude relationship.  TAS is actually how fast you are going.  In thinner air, it takes more TAS to get the same IAS (ram pressure on pitot tube, air pressure on wings).

Almost nice answer—if it wasn't for the huge error about speed of sound: speed of sound depends only on temperature, nothing else, neither density nor pressure (in the troposphere, all three decrease together, but that breaks down in tropopause where temperature, and thus speed of sound, stops decreasing and starts increasing again as you enter stratosphere).

Actually this chart shows you reach Mach 1 at lower IAS at higher Pressure altitude.  And relationship of Mach and TAS is linear, adjusted for temperature.  A little confusing at first glance though.

@RobertDiGiovanni: re "TAS is actually how fast you are going": the question is about the maximum possible speed, i.e. how fast you CAN go, not "how fast you ARE going". / re: "There is no TAS/altitude relationship."--> Above, Jimmy says: "TAS = higher/faster"

True Air Speed = how fast you are going.  Indicated Air Speed = pitot tube ram pressure at TAS, decreases with altitude for same TAS.  Mach = speed of sound at given TEMPERATURE, independent of altitude, measured in TAS.  Study that chart, it is how things were done before personal computers, cell phones, and tablets.

Then see if my answer makes sense.

You'll fly the fastest through the air at the altitude at which your VNE and your MMO match.  Higher than that, you MMO is limiting, and you can fly your MMO but your indicated airspeed will decrease as you climb -- and your TAS will decrease as well, since the speed of sound (of which you're now flying a constant fraction) is going down with the colder temperatures.  Below that crossover altitude, your VNE (i.e. limit in indicated airspeed) is limiting, and it's immaterial what the speed of sound is -- you simply can't fly faster than the VNE, and you aren't getting as much benefit from the delta between TAS and IAS at lower altitudes.
The exact point of that crossover will depend on the specific VNE and MMO of a given aircraft; typically it's around 30,000' plus or minus a thousand or two.
That is NOT where airliners typically cruise, however, because along with that max speed is a LOT of fuel flow... they'll get more miles per gallon at higher altitudes (as explained in other threads).  And also at speeds somewhat below the "barber pole" (i.e. the more limiting of VNE or MMO).  But if you want the most TAS you can get in your airliner & fuel burn be darned, somewhere around 30k and flying at VNE/MMO will be it.
If you're trying desperately to out-run a MiG on your tail and you're willing to exceed VNE and MMO (since those 'might' kill you, but the bandit certainly will), the math would get more interesting since now max thrust and "how fast you're able to go without losing control" start to enter into the picture.  And that's far enough outside the realm of realistic airline operations and pretty well into Test Pilot School stuff, that I don't think an internet forum is likely to give you any worthwhile answers there.
For practical purposes, 30,000' and flying at VNE = MMO is the answer.

It doesn’t make sense to ask for a simple answer when the question is imprecise in details and the subject matter is a little involved.
Having said that, for most civil airliners the maximum permitted speed for operations (i.e. certified limit) is the lower of VMO or MMO as explained below.
VMO (max. allowed IAS) is constant with altitude, and max. allowed Mach number MMO is, too. Maximum speed (e.g. IAS/TAS) for any given altitude is the speed corresponding to the lower of the two limits.
Maximum possible speed (i.e. if you firewall the engines and don’t care if anything breaks) can be grossly different from the above and cannot be answered in general without defining assumptions, limits and a specific aircraft due to their differences.

It is both.
There are several effects which determine the maximum speed:

At low level, a higher altitude means that the aircraft has to fly at a higher lift coefficient in order to carry its weight. This means it moves closer to the polar point of minimum drag, so it will create less drag at the same indicated airspeed. Maximum thrust drops with air density as the aircraft flies higher, so the speed increase is moderate. This is different for super- or turbocharged piston engines: Here, the maximum pressure inside the engines is limited and the boost ratio can be increased with altitude, so the available power can be maintained up to the rated altitude, so the increase in speed is more dramatic.
At low level, airspeed is mostly limited by the maximum dynamic pressure for which the aircraft is designed and gust load limits. Exceeding this limit might cause stability problems like divergence or reduced control authority, and flying too fast into a vertical gust could exceed the maximum load factor.
Another limit is flutter: Here, a maximum true airspeed limits how fast the aircraft can be flown. Certification limits must be 20% less than flutter onset speed.

At high altitude, the drag range with altitude is reversed: Now the airplane must fly at a higher lift coefficient that that of best L/D even at maximum speed, and now an increase in altitude will also increase drag at the same dynamic pressure. Now this effect runs in the same direction as the thrust loss from lower density, so the maximum possible speed drops quickly with altitude. But again, other limits might apply:

Above the maximum operating Mach number M$_\text{MO}$ buffeting will make the flight uncomfortable.
Exceeding the maximum Mach number for stability characteristics M$_\text{FC}$ reduces pitch stability below acceptable levels.
Flying above the maximum dive Mach number M$_\text{D}$ might cause excessive Mach tuck which cannot be trimmed.

Boeing 777 flight envelope (picture source)

From sea level to Ionospheres, it first increases because air drag decreases with altitude, until at a certain altitude the maximum velocity starts to decrease because engine performance decreases.

Let's apply general (...and simple) knowledge from ATPL:
There is a relationship among TAS-MN-CAS

The graph above can be used as a handy guide to the relationships between the speed
references. Of course there are some limitations (Vmo and Mmo). See the graphic below:

When climbig at constant CAS we need to change to MN from a point or we will overpass Mmo. That's the reason why TAS increases initially and then decreases as you continue climbing.

Yes the blog is correct saying that "an usually high altitude, the plane would fly slower, therefore it would have to go lower to fly faster". As J. Southworth mentioned air gets thinner as you go up, commercial aircraft engines need to pump air into engines to generate thrust. This area where you can fly at max altitude with engine producing max rate is called coffin corner.
At higher altitudes, the air density is lower than at sea level. Because of the progressive reduction in air density, as the aircraft’s altitude increases its true airspeed is progressively greater than its indicated airspeed. For example, the indicated airspeed at which an aircraft stalls can be considered constant, but the true airspeed at which it stalls increases with altitude.
Then there are drag constraints, wing designs as we go faster, B777 has turbofans that creates excessive drag because of those wide open intakes. Wing design is supercritical airfoil. These to limit it to 0.8-0.9 mach. beyond this you would be pushing the structural limits of aircraft.

The resistance of the air to the forward motion of an aircraft decreases with altitude as the air pressure and density decreases, but the power output of an air breathing power system also tends to decrease as the amount of oxygen present in a given volume of air reduces. One objective of variable air inlet design in high performance aircraft is to increase the pressure of the air entering the engine, while reducing it's velocity. The stalling speed of an aircraft also increases with altitude, so that for example the stalling speed of the Lockheed U2 at it's maximum operating altitude (about 75,000 ft) was only 2-3 knots less than it's maximum speed at that altitude. Eventually a point is reached at which the aircraft no longer has the power available to accelerate in level flight.

Speed at higher altitude with back wind will help you land earlyer ,because wind from behind add to your aircraft speed.This is the best for passagers and fuel economy.At sea level fuel compsumtion is the highest due to the density /temperature and Mach speed is lower ;true speed equal indicated /calibrated airspeed(not good for economy).

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text:
When do pilots facing bad weather turn back (U-turn)?
Passenger aircraft are not supposed to cross red areas on the weather radar. But what if the weather system is too large to circumnavigate and red areas inside the system are too large/prevalent to avoid ?

What are pilots supposed to do if the required detour around red areas would be impractically long ?

divert to an alternate airport in front of the storm (on the near side) ?
go back to the departure airport ?

Most importantly:
When/where (at what stage of the flight: e.g. PNR minus x minutes, or at a specific distance to the weather front ahead, etc.) is the decision made whether to fly through the bad weather or to abandon the destination airport ? And which criteria is this decision based on ?
I assume this decision takes place between the conflicting priorities of assuring the passengers' safety and the (real-world) pressure exerted by (some) airlines on their pilots to reach their destination airport for financial reasons ?
Please distinguish in your answer flight over land and sea, assuming different considerations apply. For example, the pilot may need to take the decision before reaching the critical point or point of no return. What are the implications of ETOPS for this question ?

The premise ("a weather system too large to circumnavigate and red areas inside the system are too large/prevalent to avoid") may be a particularly common situation when crossing the ITCZ:

 a broad band of high total precipitable water along
  the Intertropical Convergence Zone (ITCZ) (source)

Let me take AF447 as an example – not to say that red areas were unavoidable in this case, but just to illustrate how this flight through the ITCZ had to cross a weather system too large to circumnavigate entirely. Unless turning back, the pilots had to pick and choose "holes":

The top picture shows an altitude of 25,000', a radar tilt of -2 degrees, and a 160 mile range on the scope. The returns seen with those parameters are most likely to be ground returns, which is about what the display looks like.

@RalphJ thank you for pointing this out. I replaced the image.

There is no definitive, objective, commonly agreed upon set of criteria that I am aware of that provides an answer to your question.
Certainly airline dispatch departments strive to send aircraft along routes that will minimize exposure to extreme conditions if that's an option, and there may even be changes of schedules involved, but in the end, it's the aircraft captain who has to make the decision in the cockpit, in flight.
As such, and as illustrated by the answers to your previous question, individual captains will employ different criteria. In my experience in the ITCZ and given my outlook, you did your best to pick your way through avoiding the "red" if reasonably possible, and if not possible, you minimized your time in the red.
Doing a U-turn was not an option that we typically considered. This was the attitude and practice of all of my peer group save one. As I remember, he turned back once, and he subsequently left the company. By his own admission, he wasn't cut out for the type of flying we were doing.
Having to cross any of the red during en route flying was not something you had to often do. You could almost always avoid that.
And remember, what the red means is heavy precipitation, which, while potentially accompanied by severe turbulence, does not always mean that will be the case. Thunderstorms with heavy precip would sit over Victoria Harbor in Hong Kong along the IGS approach to the old Kai Tak airport, and we would shoot the approach through the red. There would be turbulence, but nothing abnormal.
Conversely, the absence of red does not ensure there will be no severe turbulence. The worst ride I ever had was going through a "clear" area the radar showed between two cells.
Concerning making a U-turn, and especially flying in the ITCZ westbound during the day, if you did a U-turn you might well find that your return route of flight has closed in and might well be worse than the forward route to your destination. If the heat of the day is building in front of you westbound, the sun's insolation has been building more behind you than in front of you.

Good answer from you, as always. re: "he left the company" – left or was gone ?

@summerrain He resigned and went to work for a start-up carrier as I remember. He reputedly had the distinction of being that captain whose list of f.o.s that he wouldn't fly with was the longest and who was on the greatest number of f.o. blacklists.

thank you. From your experience, do you think (some) airlines fire pilots (possibly under false pretenses) for keeping flights safe (and thus costly for the airlines) and being unwilling to take unnecessary risks by following the "better safe than sorry" principle, including diverting to alternate airports when other pilots are more willing to take risks or succumb to the pressure of getting the plane to its destination for fear of losing the job ?

@summerrain Personally I never observed that in any of the four U.S. airlines I flew for. I suspect it does happen or at least did in third world countries.


text:
Do pilots breathe the same air as passengers?
Do pilots breathe the same quality of air as passengers ?
(i.e. identical parameters: same O2, CO2 and O3 levels, same temperature, same humidity, etc.)
Do pilots breath the same air as passengers (shared air) ?
(i.e. the air a passenger exhales will be inhaled by the pilot [or vice verca], which also means that smoke in the cabin will inevitably end up in the cockpit)

what makes you think that this could not be the case? on which aircraft models?

In General, Yes.
As your image already shows, the same air is distributed throughout the cabin and the flight deck. For example, in the 737 NG FCOMv2 2.30.4 (Air Systems - Air Conditioning Description) it says:

Since the flight deck requires only a fraction of the air supply provided by the left
  pack, most of the left pack air output is mixed with the right pack supply and
  routed to the passenger cabin.

So on the 737, the left pack supplies air to the flight deck and the cabin, the right pack only to the cabin (in normal operations).
Air from the cabin is also reused in the recirculation system:

The recirculation fan system reduces the air conditioning system pack load and the
  engine bleed air demand. Air from the passenger cabin and electrical equipment
  bay is drawn to the forward cargo bay where it is filtered and recirculated to the
  mix manifold. The fan is driven by an AC motor. The fan operates with the recirc
  fan switch in AUTO except with both packs on and one or both in HIGH.

This implies, air previously exhaled by a passenger could make its way into the flight deck, but it is filtered first. In case of smoke in the cabin, the recirculation system would be switched off. However, during normal operations, the left pack supplies the flight deck directly:

(source: 737 NG FCOMv2 2.30.4)
All air quality parameters you mentioned should be identical or very similar for the flight deck and the cabin, except for temperature. Most aircraft allow separate temperatures for different zones. E.g. the 737 again:

There are three zones: flight deck, forward cabin and aft cabin. Desired zone
  temperature is set by adjusting the individual Temperature Selectors. The selector
  range is approximately 65°F (18°C) to 85°F (30°C).
  The packs produce an air temperature that satisfies the zone which requires the

Temperature Selectors in the 737 overhead panel:

(source: 737 NG FCOMv2 2.30.4)
The details will of course depend on the exact aircraft model!

No, they do not. The pilots in the flight deck zone receive 100% fresh conditioned air directly from the left pack. The rest of the conditioned left pack air will be collected in the mix manifold for distribution for passengers. Recirculation fans will recirculate cabin air back to the mix manifold. Since the F/D isn't receiving air from the mix manifold, they aren't receiving recirculated, stale cabin air.

This answer would benefit from some references.

Surely this would depend on the design of the particular aircraft?  In my Cherokee, for instance, passengers generally breathe the same air I do - whatever leaks in or comes in through the heater - unless I open the little vent window on the pilot's side.

For a 737, this answer is incorrect. Even with the left pack supplying the flight deck, you still get some amount of recirculated air, as demonstrated by the decrease in airflow to the cockpit when the recirc fan is switched off. The pilots get a greater proportion of their air straight from the pack than the passengers do, but it's not separated. If it were, the checklist for smoke-in-the-cabin wouldn't have pilots putting on oxygen masks & smoke goggles!

@RalphJ OP asks if the quality is the same. The amount of recirculation has effect on the quality, correct?

+1, the answer is correct


text:
Can pilots choose runway and landing direction?
Pilots normally receive landing clearance for a specific runway assigned by ATC. Absent an emergency, can pilots of commercial flights (depending on the wind conditions for example) choose

a different runway
the landing direction for this runway
or both ?

If no, why not ?
If yes, (and still assuming nothing is wrong with the aircraft) how does the pilot get his wish ? Can (s)he ..

simply choose (i.e. just communicate the choice to ATC, which has to accept it) ?
request it / ask for it (but ATC has the final say) ?
insist on it ? (analogous to "telling ATC you are altering heading for weather")

In the last 2 cases, does the pilot need to name a specific reason ?

To avoid all the Class this and that stuff, just think of controlled (tower with a clearance required) and uncontrolled airports.
If a controlled airport, the runway is assigned by the tower controller, normally based on the favorable wind.  Normally, you use the runway assigned by the controller, unless you have a reason to use another one.  Thing is, you don't HAVE to do what the controller says if it puts you in danger, and the controller doesn't HAVE to let you go where you want if it screws up his/her flow, and you could say there is always potential for a Mexican standoff situation, in theory.  In practice, there will be some mutually agreed resolution, the controller wanting everything to flow smoothly and safely, and the airplane crew wanting to get where they're going without getting violated and without being forced into something dangerous.
So say you are given a clearance to land on runway 9, landing east, but you want to land on runway 18, landing south.  So you ask for 18 and see if you get it.  The controller decides whether it will cramp his/her day and says yes or no (probably yes 99% of the time).  If no, your choices are to either land on 9, go elsewhere, or declare an emergency, in which case the decks are cleared for you but you may have to justify yourself later.  In the big picture, common sense is supposed to prevail.
At uncontrolled airports, it's uncontrolled, so knock yourself out.  You land on whatever runway you feel like, keeping in mind certain rules and protocols for uncontrolled aerodromes, like pattern (circuit) rules, IFR arrival announcement requirements etc etc.  Say everybody is landing on 9 and you want to land on 27 going the other way, forcing an airplane landing on 9 to take evasive action.   Probably you'll just get the finger from someone, but there's a possibility somebody will report you for breaking regulations on traffic etiquette and you will have to answer for it, but there is no ATC around so trouble won't come from them.

My home field is completely uncontrolled, single runway 04/22 with adjacent grass strips parallel to it. At one point when I was doing touch-and-gos on 04 in calm weather (originally the winds favored takeoff on 04, then died down almost completely), another aircraft decided to take off on 22. That made things quite interesting, to put it mildly. Nothing happened, but it definitely increased my cockpit workload for that circuit to rather close to my comfort maximum.

Pilots can request a particular runway approach course and landing but in a controlled environment they are at the mercy of ATC. At high traffic (read busy) commercial airports they are unlikely to get their request. As far as I know, shy of an emergency declaration you cannot insist on a non standard runway and expect to get it.
At a quiet class C or D airport they may very well get what they ask for. I did this a lot during my training at a quiet class D airport. If the winds were favorable to one runway but my instructor wanted to practice cross wind approaches we would request the non standard runway and if no one was around they would often grant it.

Generally you don't want to fly the non preferred runway if there are windy conditions as landing with a tail wind can be dangerous.

This perfectly answers the runway part of the question. Will mark your answer as accepted if you could also handle the "landing direction" part (i.e. land from left or right side of the chosen runway).

@summerrain you request a specific side of a given runway not a runway then a side. The phrase request a particular runway implies a given side of it. For example at KPNE there is RW 6 and RW 24 they are physically the same asphalt but requested by their headings.

Excellent. Could you incorporate this information into your answer? It would clarify this point for those who are unfamiliar with that topic.

I might need to edit the terminology used in my question. Wikipedia says: « A runway can normally be used in both directions, and is named for each direction separately: e.g., "runway 15" in one direction is "runway 33" when used in the other. » Which words can I use to distinguish between "the physical rectangular area on a land aerodrome" and "a specific side of it". It seems "runway" is used for both. Are there any more specific terms to clarify which of the two is referred to ?

In contexts where direction matters (most things related to takeoffs and landings), we consider each strip of pavement to be two different runways, e.g. Rwy 6 and Rwy 24. In contexts where it doesn't matter (like pavement type or dimensions), we consider the strip to be one runway, e.g. Rwy 6/24.

@summerrain The most important condition when landing is the wind. The controllers at the airport choose the landing direction so that the aircrafts can land against the wind leading to slower ground speed at touchdown. At an uncontrolled Airfield the pilot is the only one responsible for his action. The controllers just give advices, not instructions. So the pilot could decide to use the opposite direction, but unless being in trouble, why should he?

@StephenS: thank you. But my terminology question in the comment above attempted to find out if there are other terms than "runway" which are unambiguous (cf. "road" vs. "lane" for an analogy in road traffic). This would help me clarify this question. Maybe "strip" and "runway" ?

@summerrain One might say "strip" when the direction doesn't matter (e.g. a "single-strip airport"), but I think that's slang. "Runway" is used officially for both meanings, and context makes it obvious (to us, at least) which was intended.

@Dave: re: "you request a specific side of a given runway not a runway then a side" – yes, but it could be imaginable that if an airport has runways 6/24 and 12/30 and the pilot is cleared for 6, he could only ask for the opposite direction 24 but not the physically different runway 12/30. I take it, that's not the case. I assume if you are cleared for 6, then it doesn't matter at all which of the remaining runways you ask for (12/24/30), they all give rise to the exact same situation if asked for, correct? Your answer would benefit from mentioning this for those without foreknowledge.

@summerrain correct, this comment chain is getting a bit long and may warrant a different question but if you are cleared for 6 requesting 24 is the same as requesting 12 or 30.

@summerrain Actually, if you're cleared for 6, then presumably others are using 6 as well, so 24 is likely to be refused as unsafe, whereas 12 and/or 30 (depending on winds) have a decent chance of being approved.

[Adapted from a comment I previously posted]
I have an anecdote which bears on this, at least for the case of takeoff. In 1988 I was on a flight leaving O’Hare and the radio comms were on one of the audio channels while we waited to taxi. Among the traffic we heard was something which caused me a bit of concern: a pilot being told to use a runway he thought was too short. He started off requesting "runway ZZ" and the controller simply responded "prepare to taxi to runway AA". After a second similar request that was also refused ("ignored" may be more accurate), the pilot said, Tower, I am X thousand lbs, I need Y thousand ft, I need runway ZZ. The controller finally agreed, with real annoyance in his voice.
I've long since forgotton the exact runway numbers, and I don't know whether the current runways have evolved since that time, but then as now O'Hare was a busy place, so I can easily imagine that allowing an oddball departure on a cross runways would require significant delays. Still, I was struck by how this pilot had to really insist on the runway he needed.
Within the same 20-minute session we also heard a pilot barge into a queue, in front of a plane he was clearly (twice) told to get behind. The tower said "get in behind the Company Nine" and in this big Texas voice the pilot responded "Roger, in front of the Company Nine"; tower said "negative, behind the Company Nine" and the pilot came back "Yessir, right in front of the Nine" and the Tower just said "Ok, fine.". So maybe there's a culture of low-grade pushiness that the controllers are prepared for.
And they lost track of a plane, telling an aircraft to queue behind another that just wasn’t in the queue at all. Which objectively seems kind of odd, too, but it was the least of it that evening.

+1 thank you for the great anecdote taken right out of real life, which sometimes is different than in textbook ...

KORD had lots of intersecting runways, so an unplanned arrival or departure on the wrong one(s) is extremely disruptive--and KORD didnt have much spare capacity. Part of the recent upgrades was to remove some of those runways and replace them with more (and longer) parallels to avoid exactly this problem while increasing total capacity.

There's a similar problem at KJFK; in one particular flow, the runways used for landing are not long enough for an A380 to land when wet, forcing those flights to divert. Part or the problem is KJFK can't change their flow without KLGA and KEWR also changing theirs, and coordinating all that likely takes longer than the fuel reserves of the flight that can't land.

@StephenS: interesting, so how is the problem you describe solved at KFJK ?

@summerrain A380 flights divert to an alternate airport in that case. They avoid using that flow when the runways are wet, but sometimes there's just no choice.


text:
How to find black boxes underwater absent any pinger signals?
If CVR/FDR cannot be seen visually on the seafloor (because covered by a thick layer of mud/sediments) and no pinger signals are detected, how can they be found? Metal detectors? Any other methods?
case in point: The FDR of crashed Lion Air flight 610 was recovered on 1 Nov 2018, but 2 months later now the CVR still has not been found (while the pinger batteries are rated for 30 days only):

« The search for the CVR is hampered by thick mud. The signal source is difficult to ascertain its position considering the sea floor is mud with a depth of more than 1 meter. The ping signal from the CVR has not been received for 2 days now (5 Nov). There are other means to find the CVR however. » (source)

Which "other means" are this ?

update 18 Dec 2018: Lion Air contracts MCS to locate and recover the CVR of the 737MAX.
update 21 Dec 2018: an expert answered the question for me. I'll paraphrase his explanation as an answer below.

Or it may be attached to a larger piece of wreckage that they bring up. Once they start bringing up large sections, they can figure out the approximate location of the CVR in relation to the parts they recover. This will narrow the search area and then they can dredge to find the box if it is not part of the larger wreckage.

@RodrigodeAzevedo: My question was not how to find the haystack (huge debris field) but the needle (one specific piece) in the haystack. I hope you see the difference. Also the Titanic wreckage was easily visible on sonar images. You can find an entire debris field by ensonification, yes, but not a single piece as small as a CVR (let alone if covered by mud).

How do you find a flight recorder underwater if it isn't transmitting?  With great difficulty.

When the underwater wreckage site has already been found, but CVR/FDR are still missing, at first hydrophones are use to listen for the black box acoustic pinger signals. Absent these signals (or when they have stopped emitting after the batteries have died down), in the second stage another method is used: Sub-bottom Profiling
"High Penetration Sub-bottom Profiler":

"The systems generate high-resolution images of the sub-bottom
  stratigraphy in oceans, lakes, and rivers." (source)
"Sub-bottom profilers work by transmitting sound energy in the form of
  a short pulse towards the seabed. This sound energy is reflected from
  the seabed and the sub-surface sediment layers. The reflected energy
  intensity depends on the different densities of the sediments, the
  denser (harder) the sediments, the stronger the reflected signal. The
  reflected signal then travels back through the water to the receiver
  (either a towed hydrophone or transducer). The received signals are
  then amplified, processed and displayed in the acquisition system." (source)

  Deployment of Various Shallow-Water Sub-bottom Profiling Systems

In the case of JT610 a ROV is also used:

« The recovery team is set to utilize an ROV equipped with the needed features to search for the missing CVR that is believed to be buried
  under the seabed. “The device that we prepared is able to detect
  objects buried 4-meters under the bottom of the ocean.” » (source)

FYI, setting up questions that you already know the answers to, then providing your own answer while arguing with sincere responses, makes you come across as full of yourself and a know-it all.  This isn't the first time you have done this either.  Just my humble opinion...

The CVR on a Boeing 737 is located in the aft cargo compartment. The CVR itself is not built of the same materials as the aircraft, which is mostly aluminium and composites. By mapping the location of other components of the aircraft found in the sea bottom it should be possible to make an educated guess of the general location of the CVR (assuming the aircraft did not disintegrate, sending everything in different directions). One common way of tracking down the CVR is by using an underwater magnetometer to detect ferrous metal objects. The problem is that something as small as a CVR will only be detectable up to about 20' under the ocean floor. If it is buried deeper than that it will be difficult to find. That's why they have pingers, but those stop working when the battery runs out.

re: "it should be possible to make an educated guess of the general location of the CVR": If you look at the quote above and click on its link, you will see that the FDR of crashed Lion Air flight 610 was recovered on 1 Nov 2018, but the CVR still has not been found yet. / re: "If it is buried deeper than that it will be difficult to find." --> hence my question

re: "That's why they have pingers" : please note that the question was about cases WITHOUT pinger signal (malfunction, dead batteries, signal not detectable because CVR is covered by aircraft debris, etc.). From the same source: "The locator ping signal, believed to originate from the CVR, had died down, possibly the CVR is covered by mud". Although counter-intuitive, the pinger location is difficult to detect in shallow water.

In re: the educated guess, my answer explains itself. As to the lack of pinger signal, I read the question, I am a pilot and have worked for major airlines, I know what i am talking about and I know what you meant. The pinger is not difficult to detect in water. The sound of the pinger carries for a great distance. But sound does not carry well in mud.

To clarify, what happens when the CVR is buried is that the ping can only be heard if you are very close to the source. That's why traditional listening methods when searching for the CVR don't work if the CVR is buried.

I repeat, this question is about the case where NO pinger signal is emitted AND/OR detected! This always happens after a couple of weeks when the pinger batteries have died and can also happen already on day 1 for a multitude of reasons.

Please delete or provide evidence for your claim that "the pinger can be detected when a CVR is buried under mud". The search effort quoted in my question show that this is false.

@summerrain The search effort proves no such thing. it only proves that they could not find that CVR. Even the Indonesian authorities at Basarnas admit that the CVR can be found with the pinger if sea currents wash away at least some of the mud.
You are wrong about this as well: "This always happens after a couple of weeks when the pinger batteries have died". Modern CVR's have enough battery power for 30 days, not 2 weeks.
You seem to have some axe to grind. Do you work for Lion Ar, or are you related to anyone who was in the aircraft when it crashed?

And now, as I suspected would happen, the CVR has been found, under 8 meters (26 ft) of mud. https://edition.cnn.com/2019/01/14/asia/lion-air-cockpit-voice-recorder-intl/index.html

I don't know the details, but since there is still no good answer, I'll wager an educated guess.
Metal detectors do work under water, but I believe sonar can also scan through a layer of mud and can work from larger distance, so it can scan the debris field more effectively.
Then the mud will be sucked or blown away and the items identified visually. Usually this is done using an remotely operated submersible vehicle.

This isn't an answer and would be best posted as a comment...

And it would more likely be done using a remote-control submersible vehicle rather than an autonomous one, wouldn't it?

@Transistor, it would only be “autonomous” in the sense it does not need to be attached to the ship by a cable; of course there has to be operator watching the camera and sonar images. And in shallow waters like this it does not really need to be autonomous at all; it may well be on a cable.

@JanHudec: these are technical terms. There are ROVs (remotely operated (underwater) vehicles) and AUVs (autonomous underwater vehicles)


text:
Do special procedures exist to limit pilot workload during pilot incapacitation?
Although pilot incapacitation is rare, the website avherald.com lists several occurrances of flight crew incapacitation, alone two events reported yesterday.
FAA AC 25.1523-1 requires all aircraft to be capable of operation
by one pilot only from either seat, so just one pilot can safely fly the aircraft - albeit under increased workload.
In case of flight crew incapacitation, do airlines (or regulatory bodies?) have dedicated Standard Operating Procedures (SOPs) for the remaining pilot? Obviously, the pilot would declare PAN/Mayday and assess whether it is safer to land asap or continue. Or are there no special procedures because it happens so rarely?
Are there any procedures to limit pilot workload in these instances, such as shortened procedures, ask a cabin crew member for assistance such as reading checklists, any support from the ground / airline operation center...? The remaining pilot must execute all tasks of Pilot Flying and Pilot Monitoring, which means heavy workload during final approach.

There are no official regulations for this that I know of, but there may be airline/operator specific procedures in the SOP's. In an otherwise functional aircraft though, landing with one pilot is more workload than normal, but not outside the realm of possibility. Pilots are trained to use CRM as a tool, not a crutch. ATC will attempt to alleviate some of the workload by prioritizing/clearing traffic and help them minimize any kind of ATC instructions.

What's your big fascination with pilot incapacitation? You've got 5 different questions going, all a slight variation.

@CrossRoads: PhD research on flight deck operations, pilot fatigue and future operations....

Well, as a catch-all there is always FAR 91.3 which says he pilot in command can deviate from any regulation if they deem necessary in time of emergency in order to safely operate and land the aircraft. Obviously there's a reasonable limit to that and you'll be asked to give a report to the FAA on what happened, so be ready to defend your actions.
I can't comment on airline company procedures, but I have to assume there is a plan in place for this scenario since it is so realistically likely to happen at some point. I believe another crew member would be asked to help with simple tasks like reading checklists as you mentioned.

IIRC, it was tangentially mentioned in an answer to a different question that all cabin crew receive basic flight training which will allow them to take over some of the duties of the PM, e.g. reading checklists and operating radios.

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text:
At what minimum occupancy ratio can airlines operate profitably?
Often, airlines are unable to sell all the seats of a flight and some seats go unsold. So, with what occupancy ratio is it usually profitable for an airline to operate?
For example, Recently, a Turkish Airlines A330, flying from Bangkok to Istanbul (12,000 KM) made an emergency landing after a bomb hoax. The interesting thing was that it was carrying only 142 passengers, against its marked capacity of 250 passengers (occupancy ratio of about 0.6).
And what are the factors which would influence this choice – like probably, it would be cheaper to operate a B787 with 0.6 occupancy ratio compared to a B747.
What are some other factors which influence this?

Scheduled flights have to be operated regardless of occupancy. Only technical reasons allow airlines to cancel a flight.

An airliner may be convoyed with no payload to the beginning of its next leg. And this next leg may generate enough profite to justify this flight with no payload.

Anecdotally, I was once waiting to board for my last leg home. There were maybe 20 people waiting at the gate when they announced a delay. They continued to announce 30 minute delays until the next flight to the same destination at which time there were maybe 50 people waiting at the gate. The 2nd flight was also delayed for a couple of hours until the last flight of the day which we all boarded and took a nearly full plane. Maybe it was coincidence, but it looked like they cancelled 2 lightly booked flights to make 1 full one...

Then there's this guy who went viral 6 months ago, because he was literally the only person on the plane: http://fox13now.com/2015/01/13/man-boards-delayed-flight-discovers-i-am-literally-the-only-person-on-this-plane/

You just need one, but he has to be Bill Gates or Warren Buffett.

@PeterKämpf - Source? It may be technically illegal, but if they can find any excuse not to fly an underloaded plane, they will. I have a source in the family who works with Southwest's flight scheduling software (aka the "cancellator") and he says that when a plane is pulled for maintenance, the system will juggle the remaining flights and planes to inconvenience the fewest number of passengers possible; that means the least booked flights get cancelled and those passengers rebooked to create fuller flights. He wouldn't go so far as to say how "convenient" these maintenance pulls might be...

@KeithS: Absolutely, this happens routinely. But not officially. I've witnessed it myself when booked on the one before last connection of the day. My flight was cancelled "for safety reasons" or "for repairs", and I flew two hours later in an half-empty plane. They never ever will admit that the flight was pulled to save some money - this would alert the regulating authority.

I once travelled with only 5 passengers on the plane (myself included).. It was an A320

I also travelled on a B777-300 ER with only about 20 passengers!

@KeithS SWA canceled my (mostly empty) nonstop HOU-OKC and put us on the direct HOU-DAL-OKC leaving at the same time from the next gate over. They didn't even bother pretending it was a maintenance problem. For half the price of AA, UA or (then) CO, that's fine with me.

@PeterKämpf: re: "Scheduled flights have to be operated regardless of occupancy. Only technical reasons allow airlines to cancel a flight." – Could you source or reason this claim? This answer claims the opposite: "airlines may cancel any flight. There is no obligation to execute a specific flight.". Is that wrong?

@summerrain: Only charter airlines may cancel any flight. That is the big difference to scheduled airlines. See the Montreal Convention for more. This puts obligations on operating air carriers where cancellations should be limited to cases where an event has been caused by extraordinary circumstances which could not have been avoided even if all reasonable measures had been taken.

@PeterKämpf, the Montreal Convention obliges airlines to compensate damages due to arbitrary cancellations on international flights. It does no prohibit cancellations. There is no punishment for  cancellations.

They can operate with 0 passengers, but will most likely not generate any revenue (unless cargo is carried to generate additional revenue). Revenue and profit on a passenger flight (assuming no paid cargo) will be based upon how many tickets were sold at which price, so the number of passengers required for any given flight to break even will be variable and cannot be answered in a general way.

Note that they could still run a profit by selling seats to travel agencies. If they can't fill pre-purchased seats (for instance when terror alerts suddenly lead to mass cancellations) the airline is still paid and it's the agency that takes a loss.

I have reworded the question...

@anshabhi As SentryRaven said, it will vary and will not be answerable in a general way. For example, there are several routes in the U.S. that are usually flown almost empty, but with high per-seat fares and/or government subsidies in order to provide air carrier service to remote areas. On the other hand, routes with lots of competition will usually need high occupancy ratios to be profitable.

Generally, it is a load factor of roughly 70%, but the answer depends on many factors. Also, many airlines operate a fleet of different types of aircraft so the answer is never easy.
100% load factor @ 100 seats × \$100/seat = \$10,000.
\$10,000 − operating costs (fixed and variable) = profit per flight.
One you add in aircraft type, ancillary revenues, and total amount of flights, and the routes/network, the answer gets very complicated.

Can you provide a citation to the 70% claim?

With fares per seat on the exact same plane known to vary by a factor of 20+, that methodology is doomed to failure. A flight could be profitable with the right ten passengers or unprofitable with the wrong one hundred passengers.

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text:
If both pilots are incapacitated, what happens?
How do the airlines prepare for a situation where for some reason both PIC and SIC are incapacitated for the remainder of the flight?

Related question

What happens? Unfortunately something close to Helios 522

It's all explained at the end of this: https://www.youtube.com/watch?v=rQbj9uvYL8I

How do GreyHound and Amtrack prepare for both drivers to be incapacitated?  Oh... they only have one driver to begin with?

@abelenky Amtrak (nearly all trains, actually) is a really bad example: Train systems are designed to deal with incapacitation using dead-man switches. The train will brake itself to a stop, and the block signaling system will indicate the track is occupied to prevent other trains from crashing into the one that's stopped. It's actually incredibly hard to crash two trains into each other. Implementing equivalent functionality for aircraft is much harder, because planes don't run on tracks…

@SteliosAdamantidis To be fair, in that incident, the person didn't enter the cockpit until almost the exact same time that an engine flamed out from fuel starvation and the person was probably also still suffering, at least somewhat, from hypoxia.

How does Airbus prepare for a dual engine failure on the A320?
The short answer is this isn't something that's realistically planned for because the chance of a double-failure of the redundant systems in question (the two pilots) is pretty unlikely, and many of the conditions that could lead to it would result in a catastrophic loss of the aircraft anyway.
(The most notable exception to that would be a loss of pressurization at altitude, in which case hopefully at least one of the pilots can get their oxygen mask on to make the emergency descent.)

The ATC/Airline system as a whole can theoretically deal with this sort of a double failure in a few different ways. The most common is finding an off-duty employee of the airline who is riding non-revenue (dead-head, jumpseat, etc.) to fill the role of an incapacitated crew member.
This is of course predicated on whatever incapacitated the flight crew not affecting this other person.
If no qualified personnel are available it may be possible to get an experienced instructor on the radio to "talk the plane down", but that relies on having someone onboard who can (a) get access to the cockpit, and (b) at least figure out how to operate the radios to ask for help.
"Talk-Down Landings" have happened in small aircraft on several occasions, but as best I can determine this has never happened in a transport-category aircraft (airliner) outside of simulations and similar thought experiments.

In response to the second paragraph, there was Helios 522...

@raptortech97 I'm sure that's not the only case of dual-pilot incapacitation either, but I bet you'd have a hard time naming 5 without really digging. It's an incredibly rare event, and solutions are pretty hard to make workable (anything that would incapacitate a 2-person crew would likely incapacitate a 3-person crew, so adding more people doesn't help, and solutions get more difficult to implement from there).

@voretaq7, an ability to remote-control the plane from the ground, like a drone, would do it.

@AE Remote control of airliners will happen as soon as someone can implement it securely (it needs to be literally unhackable or someone will crash a plane into a building with it), reliably (at least as reliable as a second pilot), and cheaply (it has to cost less than a second pilot). In other words, "not any time soon".

@voretaq7, I was thinking about those things - or security and reliability at least - when I made my comment, and what I thought was: surely war-drones must be secure (or as secure as they can be) and reliable? Because otherwise the enemy would take control of them. Which (as far as we know) has never happened.

@AE http://en.wikipedia.org/wiki/Iran–U.S._RQ-170_incident

@voretaq7 - oh! - interesting!

@AE - Any remote electronic device is "hackable" once you get one hand on the software and/or hardware scheme. High level of secured system is likely to be non standard, advanced, proprietary, and sometimes classified technology. Put that in a common place (airplane) and you'll be hacked 10000 times faster. I don't claim the RQ170 incident is true story (reverse engineering of this level is likely unbelievable) Anyway, remotely taking control in mid flight is already an hack to begin with. To secure that, you'll have to confirm the control delegate from the airplane itself, but wait..... :/

I suppose one solution would be to implement remote control with a physical disconnect accessible to the pilots. Also, it would need to give the pilots an extremely noticeable warning upon its activation and should be automatically disabled during critical flight phases. It should also probably give the pilots a warning for, say, 60 seconds before going active, so that they have a chance to stop it before control is gained in the case of a hack.

Well this goes against what I have been told on here, that it would be impossible for an untrained person to be talked down to landing an A320 (Something I was hoping to train in)

In the highly unlikely event of this, a person who knows something about planes would get instructions from ATC of how to fly. A few years back there was a helios A320 which had a pressurisation issue. Everyone was un conscious and a member of the cabin crew attempted to land the plane. Thou, it was un successful. To sum up, ATC Would instruct someone how to fly and then auto land the plane, and this would most likely never happen.


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Anyone estimating possible paths of MH370 quantitatively?
I had posted the question below on a New York Times article, but did not get any useful replies.
The series of six successful Inmarsat pings known to exist, MAY carry enough information to say if the plane most likely went along the S or the N arc we see in reports. Unfortunately, only the last ping (at 8:11AM) is available publicly.
Here is the basic idea on extracting the information: A Malaysian military satellite gave the last geographic fix of ML370 at 2:15AM. A circle can be drawn with this point as the center and distance traveled at maximum speed as diameter, confining the plane's position at 3:11AM. From the ping at 3:11AM, another circle can be drawn, like the one drawn at 8:11AM. The intersection of the two circles give an arc of most likely 3:11 AM positions.
At 4:11AM, we will have a series of circles from max distance and one circle from the ping. These intersections will give a series of possible arcs.
This process can be repeated (with increasing complexity, of course) giving us a series of most likely positions at 3:11AM, 4:11AM, 5:11AM, etc. If the trajectory of these sequence of spaces has a N/S directionality, we can say with some confidence that the aircraft went that way.
In reality, this would be more complicated. For example, the plane most probably did not go along a straight path at max speed. However, useful inferences can be made by adding other information available. For example, from the ping circles separated by one hour, we can get plausible directions the plane may have taken. Why isn't anyone pursuing this line of analysis?
There is a bit more detail here. Anyone estimating possible paths of MH370 quantitatively?

how do you think australia got it's estimate for the newest search area

Please do not reply by email. The goal of this site is to build up a repository of high-quality questions and answers for everybody to refer to. Sending answers privately to the asker completely circumvents this.

@unni re: "From the ping at 3:11AM, another circle can be drawn". The ping doesn't give you geographical locations of the aircraft transmitting the ping, but 3 types of data: The time, the burst time offset and the burst frequency offset. So where do you want this circle to be drawn? Yes from these trifecta of data you can calculate circles, but these are concentric, not intersecting: https://i.sstatic.net/sBpbo.png Also at 3:11 AM there was no ping. The ping closest in time occured at 3:41 MYT = 19:41 UTC.


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Has a commercial airliner ever ditched in an ocean resulting in a successful water landing?
They have rafts and life jackets on board and before takeoff, passengers are explained how to use that equipment, but have any evacuations ever happened successfully?

in a river and off the coast have happened

Some plane don't have rafts; In this accident:http://en.wikipedia.org/wiki/Tuninter_Flight_1153 passengers climbed on the wings to stay afloat.

Although rafts wouldn't have saved most of the people who died on that flight because they were unable to reach the doors due to their injuries.

Yes, commercial airplanes have landed or crash landed in water many times.
If I am not mistaken, you are asking about scenarios when the on-board life jackets and life raft are used.
Here is a list of water landings. Examples when a life raft was used are (in addition to ratchet freak's mentions):

On 22 October 1962, a Northwest Airlines DC-7C with 7 crew and 95
  passengers made a successful water landing in Sitka Sound. ... The
  plane stayed afloat for 24 minutes after coming to rest in the water,
  giving the occupants ample time to evacuate into life-rafts.
In 1993, China Airlines Flight 605, a Boeing 747–409, ended up in
  water after it overran runway 13 ... All of the 396 occupants donned
  life-vests, boarded the eight slide/rafts and no fatalities resulted.

I don't think "ocean" and "water" mean the same thing.

Yes - it happened in 2009 in the Hudson (well it's a river), and it happened in 1996 Ethiopian Airlines Flight 961 as far as I know.

Sadly, Flight 961 was a lesson in why safety briefings do matter.  Many people died because they inflated their life jackets whilst they were still inside the aircraft and could not escape.

BTW. is there a way to deflate the jacket? I've never been briefed on that, and I'm always thinking that at least a few people will surely inflate it before getting out.

@domen yes, you can deflate the life-jacket using a valve. You can also inflate it again using the same valve. At least with the flights I took recently that was always on the briefing.

@AndréStannek: While I have been hearing a remark about the ability to use valves on the jacket to add and remove air during the briefings for years, I had always interpreted that as a slight adjustment of the basically inflated jacket. It had never occurred to me that this was supposed to mean that the jacket can be totally deflated like this. Thanks for the hint, I suppose the briefings should make that option more explicit.

@O.R.Mapper it's pretty much like a beach ball. If you squeeze the valve open you can squeeze the air out of the life jacket, or blow more in.

I've never been briefed as passenger with instructions on how to deflate the life-jacket. Safety announcements only warns not to inflate it while still inside the fuselage. When I didn't knew how to deflate it, I assumed I had to make a hole for the air to escape (while you can't bring any sharp object in cabin.. I would have tried a pencil without much confidence it would work) - A stew even told me if a passenger can't escape the sinking wreckage due to inflated jacket, he would be part of the loss; they were not trained (yet) to provide such instructions in the general safety anouncement.

Yes. A Cathay Pacific DC-4 (technically a C-54) was shot down by Chinese fighters off the coast of Hainan island on 23 July 1954. With his rudder and right aileron shot off, fuel tanks on fire, and the #4 engine down, the pilot ditched into the ocean. Of the 19 people on board (including 3 flight crew and 3 cabin crew,) 9 died either from bullets or the ditching into the ocean. The remaining 10 floated in the water for a while and then inflated and boarded one of the rafts. The passengers remained on board the raft for several hours until a USAF SA-16 Albatross flying boat was finally able to find a spot were it could land on the rough seas, then taxied to the raft and pulled everyone on board before taking off and flying to Hong Kong. A passenger who had been badly injured died en route to Hong Kong. The remaining 9 people survived.

Yes there have been several such instances. To name a few, some of which were captured on camera:

Ethiopian Airlines Flight 961. You can see the actual crash landing video here. 125 of the 175 passengers and crew on board died.
US Airways flight 1549. The video was caught on a cctv video. All passengers and crew were safe.
Tuninter Flight 1153. 23 out of 39 survived. No film exists but it was dramatized in a Mayday episode here.

There have been many other evacuations, some successful and some not so successful. You can get a detailed list here.

I'm not sure if this fits in with "commercial airline", but there was also a Cessna 208 "Grand Caravan" that crashed just off the coast of Kalaupapa, Molokai, Hawaii about a year ago on December 11, 2013. It made an emergency landing into the Pacific Ocean after the engine failed just after take off. The aircraft was chartered by Makani Kai Air to deliver passengers from Kalaupapa to Honolulu. One person (a state health department director) was killed in the crash. The crash was also captured on video with a GoPro camera by one of the passengers.

One more for you: an SAS DC-8 crash landed in Santa Monica bay in January of 1969. Most of the crew and passengers survived, using the on-board life rafts. There were some issues as two of the rafts were punctured by debris. The survivors (30 out of 45 aboard) were rescued after about an hour.
The cause was controlled flight into terrain resulting from flight crew failures and a series of issues including an inoperative nose gear light which distracted the crew.
The tail struck first and broke off, sinking immediately. My dad had been a purser for the airline in the late 1940s and I remember him telling me that one of the victims sitting in the crew seats in the tail was an old friend with whom he had flown. My dad was pretty upset to lose a friend this way.

Pan am flight 6 often mistakenly called flight 943 crashed in the Pacific Ocean half way between Honolulu and San Francisco. All 24 passengers and 7 crew members were rescued by the coast guard and survived. The crew members on the pontchartrain are true heroes. My father was on of them. The incident happened October 15th 1956. They lost 2 of their 4 engines around 3:00 a.m. they flew circles to burn off fuel and wait for daylight. They hit the water at 8:15 a.m.. the plane split in half but Coasties were there within minutes.

Technically an answer but can you reference the specific accident from another source.

Jerry, welcome!  You are correct that all the HUMAN passengers and crew survived.  Pan Am 6 also carried 44 cases of live canaries and sadly, none of them survived.  source: Wikipedia

Good answer by me!

ALM Antillean Airlines Flight 980 was a flight scheduled to fly from John F. Kennedy International Airport in New York City to Princess Juliana International Airport in St. Maarten, Netherlands Antilles, on 2 May 1970. After several unsuccessful landing attempts, the aircraft's fuel was exhausted and it made a forced water landing (ditching) in the Caribbean Sea 48 km (30 miles) off St. Croix, with 23 fatalities and 40 survivors. The accident is one of a small number of intentional water ditchings of jet airliners


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How does the weather radar work?
I was reading this question about turbulence and how pilots foresee it, and in one of the answers, @Rhino Driver states:

Weather Radar Just like using your eyes, except the radar can see further through haze and other clouds. Typically this is useful for finding embedded thunderstorms, but it can also be useful to find areas of potential turbulence

And that make me wonder...

How does the airliner's on-board weather radar work?
Is it connected to ground base stations to synchronize the weather info?
What kind of "weather types" can it detect? (i.e. thunderstorms, light rain, clear weather)

It works the same way any radar works.  An antenna broadcasts a pulse of energy and listens for its reflection and interprets the power of the reflection to calculate the reflectivity factor Z, expressed in decibels dBZ (helpful because return power varies across many orders of magnitude).  Weather radar can see water, hail, bugs, birds, bats and bigger things, and the ground but not clouds.  Higher return power can mean more objects or bigger objects.  A basic single-polarization radar cannot tell the difference between a tons of small rain drops and a fewer big raindrops.
The particulars of the radar on any aircraft are generally going to be determined by the antenna size, as the optimal frequency of emission varies for a given antenna.  The large S-band* dishes that make up the ground based WSR-88D network are quite big (around 10m).  S-band is a good choice because they have low attenuation and can penetrate through storms and see things behind them.  Airplanes can't use S-band though, because the antennas are too big to put on the airplane and require too much power to fully utilize them.
Airplane radars are generally in the X-band*.  X-band can see smaller particles than S-band but attenuates easier.  This means if a big storm is in front of you, the energy doesn't penetrate far into the storm and may not show you the whole storm.  These are great short range radars and work well in airborne applications as long as you are aware of the issue with attenuation.
Airplane radar displays typically only display information from the on-board radar and do not downlink any additional information from ground stations.  Onboard radar are usually adjustable in the vertical by the pilots, so they can point the radar up or down as needed.
Here is an example of a radar antenna and associated electronics on a Cessna Citation 501:

Image by Dtom, Wikimedia Commons.   https://en.wikipedia.org/wiki/File:Cessna501_radar.JPG
*S-band is 8-15 cm / 2-4 GHz
 X-band is 2.5-4 cm / 8-12 GHz

I love the "handle like eggs" on the black thing.

They are not connected to the ground, they are RADARs and operate independently.
The RADAR sends pulses, typically in the 10cm or 5cm range, which are reflected by water droplets.  The greater the concentration of droplets, the more the reflection (more power returned to the RADAR) which is used to provide the colours. Green means light density, orange means medium and red high.  Not shown is magenta (or purple) which is the really nasty stuff.
Some weather RADARs also use the Doppler effect to show relative wind speed and turbulence in these areas.
Clear air is where there is no colour between you and the first return (first bit of colour).  As DeltaLima correctly states below, it is possible for the signal to be attenuated so much that there is nothing to paint so no colour beyond the first return cannot be interpreted as clear air.
They can detect rain, thunderstorms etc and some models, turbulence.  You can also change the "gain" of the receiver to produce different displays to better see the bad stuff and can often be tilted up and down to see what's above or below and to get some sense of how high a storm is.

No colour does not mean clean air. Dense cells attenuate the signal so much that you can't see through them. The air behind the dense cell does not get painted on the display but isn't clean at all. In fact you look at unpainted areas to distinguish ground reflections from cities from dense rain cells. Cities don't leave a radar shadow, rain cells do

Do you know of any civil non-research airborne Doppler radars?  I'm not familiar with many airplanes but the ones I am do not have Doppler capability.

@DeltaLima We're both kind of right (ex RADAR engineer here), the "no colour" between you and the first return is clear.  I'll edit to clarify.  Thanks,

@casey  I don't have first hand experience of civilian use but I know they exist.  Here's one.  I think they are used in the NASA storm research C130s. The Nimrod AWACS also had one but I cannot recall the details.  I believe it was a Marconi set and I'm searching for references.  I'll add detail if I find it.

@casey Here's another example

@Simon Nice, that is one fancy airborne radar.

@casey Sure is!  I stopped working on that kind of stuff when klystrons and magnetrons (powered by a steam engine) were the order of the day ;)


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Can the FDR be interfered with in-flight?
Can an FDR on a Boeing 777 be interfered with or vandalised during flight?
If this has happened on MH370 then the black boxes may not yield any data if found.

you can pull the fuses of the black boxes, this may set off an alarm depending on the craft though


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Is the air in aircraft cabin toxic?
I just listened to the recent BBC podcast episode Aerotoxicity: the hidden dangers of flying and there were interesting claims there:

Cabin air in modern passenger aircrafts comes directly from engines (it's called bleed air).
This air is unfiltered and during so called fume events it may contain toxins from engine oil and other fluids. These toxins are called Tricresyl phosphate and persons exposed to them for a long time may suffer diseases of nervous systems, from psychological problems like depressions to neurological symptoms, like unexplained pains, severe headaches, etc.

As they said in the podcast, there are allegations that these

...fume events have not only made many ill, but they are being blamed for premature deaths

and that there are

...hundreds of legal cases going through the court.

I have never heard about this danger before and I consider the BBC to be very reliable source of information, so it surprised me. Are you aware of any study which would prove this danger?

Might be better suited to [skeptics.se] as this is not really about Aviation, more about debunking a notable claim (Reliable or not, BBC is a notable source)

You forgot claim #3 about chemtrails..

Fume exposure usually comes from Auxiliary Power Units because oil gets into the APU's bleed discharge more readily and stinks things up.  Anyway, it's all become blah blah blah blah... blame this blame that, yet life expectancy gets longer and longer.  It's an industry unto itself.

@Jamiec.  Not about aviation? Better suited to skeptics? It’s a fact the cabin air comes from the engine, it’s a fact that fume events occur. See here: http://avherald.com/h?search_term=Fume&opt=0&dosearch=1&search.x=0&search.y=0. These events are about aviation, and are real, nothing skeptical at all. Just because something is infrequent, doesn’t mean it’s not real. Fume events are as common as engine shut downs, which are also not a conspiracy theory. Cheers.

It seems this is a fairly new issue cropping up and I have been able to find some credible research on the topic (i.e. from official aviation authorities and not news outlets or lawyers websites...) but all of it is pretty recent. The CAA seems to be aware of the issue and has some information on it here. The two studies they link were published in 2017 so the topic seems to be recent, you can find the full text here and here.
The Australian authorities via CASA conducted a pretty hefty study on the topic in 2007 and came up with a list of 37 recommendations which includes the development of an anonymous online reporting system.

That the Australian Government, through CASA and the ATSB, sponsor and
  fund the development of a single, central, internet-based,
  confidential reporting system on cabin air contamination incidents to
  be co-ordinated and operated jointly by CASA and the ATSB. To improve
  the reporting and monitoring of cabin air contamination incidents,
  this system should have web-based forms to facilitate the collection
  and collation of data from all authorities and companies responsible
  for cabin air contamination incidents that would enable the data to be
  tabulated into a de-identified and unalterable uniform document that
  could be accessed and utilized by all stakeholders.

They also are setting some resources aside for studying long and short term effects of an event

That CASA in association with the Department of Health and Ageing
  (DOHA), the Institute of Health and Welfare or the NHMRC sponsor a
  project to define possible criteria for case definitions for short
  term and longer term health outcomes following episodes of cabin air
  contamination.

Clearly the CASA sees this as a real issue.
The FAA published a safety advisory on the topic in March 2018 and is clearly acknowledging the issue.
Its worth noting that most of these studies and claims refer to an "event" in other words a notable time when there was a fume event implying that this is not a constant occurrence. On the flip side, cabin air is actually pretty clean, as discussed here and researched here. Interestingly this CDC study seems to point to the slightly lower oxygen levels and more importantly tight quarters with a lot of other people to be factors in health issues on aircraft. They did this by comparing flight attendants with teachers who also work in lower circulation, high person density environments.

As an additional note, the 787 Dreamliner is the first aircraft to obtain cabin air from a seperate compressor specifically designed for that reason, rather than rely on compressed air from the engine.


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Will an Airbus A320 plane go into an unrecoverable nosedive and crash if a single angle of attack sensor fails, like on Lion Air JT610?
For example, has an Airbus gone from cruise flight into an automated unrecoverable nose dive until it hit the ground because an AOA sensor failed in flight?
Moreso, are there any cases of an AOA sensor failing on an Airbus, and the plane not crashing?

Air France 447 (though outcome was much due to pilot error)?

Yeah that was due to the pilots stalling the plane, not automation forcing the plane to go from cruise flight to a nosedive till it impacts the ground like the Lion Air flight.

But as I recall, the initial condition was created because of a frozen AoA sensor.

Airspeed sensors. This disconnected the autopilot and shut off the plane's automated protection systems, and the co pilot (Bonin) then inexplicably pulled the nose up and made the plane stall. So it was kind of the opposite of what happened to Flight 610.

447 was because the pilots became focused on wild and crazy airspeed indications and failed to go back to their basic IFR skills of flying pitch attitude and altitude when the speed indications don't make sense, and eventually becoming mentally saturated, confused, and settling into a mental "tunnel vision" state.  The right seater was in total panic mode and had the side stick at the aft limit almost all the way down, and the left seater didn't think to override him.

You're absolutely correct. Sorry 'bout the foggy memory.

IIRC the basic cause was thought to be airspeed fluctuations caused by ice crystal accumulation in the pitot probes.  The crystals build up at the first bend in the pipe, away from the heated portion which is only near the tip.  Bizarre how that particular phenomenon only started to show up in incidents over the last 10 or 15 years or so.  Everybody provides pitch and power tables for crews to fly with unreliable airspeed indications nowadays.

Related: https://en.wikipedia.org/wiki/XL_Airways_Germany_Flight_888T

You are making an assumption about the cause of the accident of JT610. There is not a final report, yet. While your assumption is a probable cause, it’s not yet confirmed as being the sole cause, or a contributing cause.

if a single angle of attack sensor fails

No.
An A320 has three AoA sensors. If one reports a different value to the other two, the avionics will ignore values from that AoA sensor and use the values from the other two.

If two of the three fail and report consistent values - the avionics will believe the third is the odd-one out and unreliable.
If those two both both report a consistent and  overly high AoA then the flight protections will apply a nose-down input in an attempt to restore the AoA to normal values and prevent a stall. this input is averaged with the pilot's inputs.
As I understand it all the following conditions must be met for the AoA protections to be erroneously invoked and cause a nose-down input:

Two AoA sensors fail and
Both report the same value and
The value is one that would cause a stall if true.

According to Airbus' Safety-First magazine:

In normal law, on a protected aircraft, exceeding the AOA value of the
   α PROT threshold would immediately trigger the
  high AOA protection, thus resulting in a nose down pitch rate ordered by the
  flight control laws. Further increasing the AOA by maintaining full back stick
  would eventually result in reaching the α MAX threshold.

are there any cases of an AOA sensor failing on an Airbus, and the plane not crashing?

I expect there are many.
There are even cases of two AoA sensors simultaneously failing and the aircraft continuing, after some control problems.
For example this incident  reported by Aviation Week

German investigators studying the cause of an uncommanded pitch-down of a Lufthansa Airbus A321-200 near Pamplona, Spain, in November 2014, hope to discover the probability of similar events linked to frozen angle-of-attack (AOA) sensors as the investigation continues. In the interim, both the European Aviation Safety Agency (EASA) and Airbus have published directives alerting pilots of the issue and the workarounds.

...

The captain continued to hold “more than 50%” rearward stick in stable flight for a period, but with help from technicians on the ground, the crew was able to reconfigure the automation into the aircraft’s alternate control law, rather than its normal “direct” law. The action removed the alpha-protection checks and canceled the nose-down input. The aircraft then continued to its destination.

...

Airbus in early December issued a Flight Operations Transmission and Operations Engineering Bulletin to all A320-family aircraft operators noting that “if two or three AOA probes are blocked at the same angle, an increase of the Mach number may activate high-angle-of-attack protection,” which results in “continuous nose-down pitch rate that may not be stopped with backward sidestick inputs, even in the full backward position.” The recommended fix is to turn off two of the three ADRs, which puts the aircraft in alternative control law, deactivating the high AOA protection.

Great answer. Thank you!

It's also possible to calculate AoA from vertical rate, ground speed, and pitch as well, and forget those unreliable alpha sensors.